Electrochemical capacitors are characterized as having advantages, such as the abilities to provide high power and high energy, to charge and discharge speedily, and to achieve a high capacity for electrical energy storage.
An asymmetric pseudocapacitor is one type of the electrochemical capacitors, and stores electrical energy by charging an interface between an electrode of the asymmetric pseudocapacitor and an electrolyte through Faradaic reaction.
FIG. 1 illustrates a conventional asymmetric pseudocapacitor that includes an anode plate 11, a cathode plate 12, and a separator 13 disposed between the anode plate 11 and the cathode plate 12.
The anode plate 11 includes a first conductive substrate 111, an anode thin film 112 disposed on the conductive substrate 111, and a first adhesive 113 disposed between the first conductive substrate 111 and the anode thin film 112 to adhere the anode thin film 112 to the first conductive substrate 111.
The cathode plate 12 includes a second conductive substrate 121, a cathode thin film 122, and a second adhesive 123 disposed between the second conductive substrate 121 and the cathode thin film 122 to adhere the cathode thin film 122 to the second conductive substrate 121.
The method of making the conventional asymmetric pseudocapacitor is described below:
(a) adhering the anode thin film 112 to the first conductive substrate 111 through the first adhesive 113 to form the anode plate 11;
(b) adhering the cathode thin film 122 to the second conductive substrate 121 through the second adhesive 123 to form the cathode plate 12; and
(c) disposing the separator 13 between the anode thin film 112 and the cathode thin film 122.
Since the first and second adhesives 113, 123 are nonconductive, charge-transfer resistances of the cathode plate 12 and the anode plate 11 may undesirably increase, thereby adversely affecting the performance and efficiency of the conventional asymmetric pseudocapacitor.
In order to solve the above-mentioned problem, one solution was proposed to form the anode thin film and the cathode thin film directly and respectively onto the substrates by electrophoretic deposition, so that the aforesaid first and second adhesives 113, 123 can be omitted. In addition, in order to increase electrophoretic mobility of an electrolyte, a surfactant is normally added in the electrolyte. After the formation of the anode and cathode thin films, the electrolyte is removed by evaporation. However, the surfactant cannot be removed along with the electrolyte by evaporation and remains on the anode and cathode thin films, which results in an increase in the charge-transfer resistances of the anode plate and the cathode plate.